This invention relates to a Faraday type magnetohydrodynamic power generator (abbreviated MHD power generator) for converting the energy of a plasma stream directly into an electrical energy based on the principle of the electromagnetic induction of Faraday, and in particular to a cooled-electrode type MHD power generator.
A generally known conventional MHD power generator of the Faraday type has first and second electrode units 1 and 2 as shown in FIG. 1. The first electrode unit 1 comprises a first segmented electrode 4 made of non-magnetic material and disposed at regular intervals and electrically insulating spacers 6 each disposed between the segmented electrodes to mechanically join the adjacent segments together. Likewise, the second electrode unit 2 comprises a second segmented electrode 8 made of non-magnetic material and disposed at regular intervals and electrically insulating spacers 10 each disposed between the segmented electrodes to mechanically join the adjacent segments together. The first and second electrode units 1 and 2 are such that the corresponding first and second segmented electrodes 4 and 8 face each other. A pair of insulating plates 14, 16 are mounted i.e. one on the upper surface of the electrode unit 1 and the other on the lower surface of the electrode unit 2 to define a passage 9 through which a plasma flows from a known plasma generating source 3. A load 18 is connected between each of the first segmented electrode 4 and the corresponding second segmented electrode 8 through lead wires so that electric current passes through each load 18. In the plasma passage or spacing 9 between the first and second units 1 and 2 a magnetic field as indicated by an arrow 20 is supplied from a magnet. The magnet is an iron core electromagnet, as shown in FIG. 2, which includes a pair of pole pieces 22, 24 between which the plasma spacing may be provided. Alternatively, a pair of air core, or superconducting magnetic coils 26, 28 may be arranged, as shown in FIG. 3, in proximity to the mutually confronting segmented electrodes 4 and 8. Since the segmented electrodes 4 and 8 are in contact with a hot plasma stream, they are cooled by a well-known cooling device 5 in FIG. 1 to permit a continuous operation for a long time period. With X representing the direction of plasma stream as shown in FIG. 1, Y the direction in which a plane including the electrodes 4 and 8 perpendicular to the X direction extends, and Z the direction orthogonal to the plane, a magnetic field will be created, as indicated by an arrow 20, in the Z direction.
In the above-mentioned MHD generator a magnetic field is applied to the passage 9 to create a uniform magnetic density in the passage 9 between the first and second electrode units 1 and 2. When a weakly ionized plasma stream of 2500 to 2800 K flows from the plasma stream generating source in the X-direction i.e., in the direction indicated by an arrow 12, an electric field (E=V.times.B) is induced in the direction orthogonal to the plasma flow velocity V and magnetic flux density vector B and an electric current having an electric current density J will flow in the direction of the vector J. As a result, electric current having a predetermined value flows through the load 18, causing an MHD power generation.
With the direction X, Y and Z representing unit vectors X, Y and Z,
V=XV for stream flux vector (X direction, function of Y) PA1 B=ZB for (Z direction, function of Y) PA1 V.times.B=-YVB for induced electric field vector (-Y direction, function of Y) PA1 J=XJ.sub.X +YJ.sub.X for current density vector (in the X, Y plane, J.sub.X, J.sub.Y are a function of X, Y) PA1 E=XE.sub.X +YE.sub.Y for electric field vector (in the X, Y plane, E.sub.X, E.sub.Y are a function of X, Y)
Based on the view that it is preferred that with the conventional MHD generator the magnetic flux density be distributed as uniformly as possible in the spacing between the electrode units, use has been made of a non-magnetic material, such as copper, stainless steel, or ceramics which imparts no influence to the distribution of the applied magnetic flux density. The conventional MHD generator has its electrodes cooled during a long continuous operation so as to prevent damage and melting of the electrodes 4, 8. There have been arguments that the achievement of the uniform magnetic flux density distribution and cooling of the electrodes cause the power generating capability of the MHD power generator to be reduced to a practically intolerable level. The inventors have already reported in the Sixth International Conference on Magnetohydrodynamic Electrical power Generation that such a problem is solved by applying a theoretically non-uniform magnetic flux density distribution between the electrode units 1 and 2. For further details reference should be made to CONF-750601-pl vol. 1-Open cycle Generators and Systems, "The configuration of Applied Magnetic Induction for Equilibrium MHD Power Generator" pp 399 to 418. At the time of announcement of this paper a means for achieving a predetermined magnetic flux density distribution has not been realized and hence it still has been difficult to improve the power generating capability of the MHD generator.